My favorite is Eryngium alpinum.. You can easily tell it apart from planum, when you purchase by mail order & it breaks dormancy. The Alpine has heart shaped leaves, (somewhat triangular) with very serrated edges & pointed leaf tip.
Whereas, the more common - planum- has oval shaped leaves, with less serrated leaf margins & lacks the distinct point at the leaf tip.
It is often "substituted" as the seeds are easily grown, more like a weed than the more difficult to germinate alpinum species. The seeds of planum, are much less expensive, too, while alpinum seed usually requires stratification, unless you are able to germinate warm, as if it just fallen after becoming ripe on bract in warmer weater, before it would naturally get cool, up in the Alps of Europe, in nature.. I will try to get a photo for you
